土木工程外文翻譯

1、<p>　　4.1 INVESTIGATION OF STRUCTURAL BEHAVIOR</p><p>　　Investigating how structures behave is an important part of structural design: it provides a basis for ensuring the adequacy and safety of a desi

2、gn, In this section I discuss structural investigation in general. As I do throughout this book. I focus on material relevant to structural design tasks. </p><p>　　Purpose of Investigation </p><p

3、>　　Most structures exist because they are needed. Any evaluation of a structure thus must begin with an analysis of how effectively the structure meets the usage requirements. </p><p>　　Designers must con

4、sider the following three factors: </p><p>　　Functionality. or the general physical relationships of the structure's form. detail. durability. fire resistance. deformation resistance. and so on. </p&

5、gt;<p>　　Feasibility. including cost. availability of materials and products. and practicality of construction. </p><p>　　Safety. or capacity 10 resist anticipated loads. </p><p><b&g

6、t;　　Means </b></p><p>　　An investigation of a fully defined structure involves the following: </p><p>　　Determine the structure's physical being-materials, form, scale. orientation. l

7、ocation. support conditions, and internal character and detail. </p><p>　　Determine the demands placed on the structure-that is. loads. </p><p>　　Determine the structure's deformation limits

8、. </p><p>　　Determine the structure's load response-how it handles internal forces and stresses and significant deformations. </p><p>　　Evaluate whether the structure can safely handle the r

9、equired structural tasks. </p><p>　　Investigation may take several forms. You can </p><p>　　Visualize graphically the structure's deformation under load. </p><p>　　Manipulate m

10、athematical models. </p><p>　　Test the structure or a scaled model, measuring its responses to loads. </p><p>　　When precise quantitative evaluations are required. use mathematical models based

11、 on reliable theories or directly measure physical responses. Ordinarily. mathematical modeling precedes any actual construction-even of a test model. Limit direct measurementto experimental studies or to verifying unte

12、sted theories or design methods. </p><p>　　Visual Aids </p><p>　　In this book, I emphasize graphical visualization; sketches arc invaluable learning and problem-solving aids. Three types of grap

13、hics are most useful: the free-body diagram. the exaggerated profile of a load-deformed structure. and the scaled pial. </p><p>　　A free-body diagram combines a picture of an isolated physical clemen I with

14、representations of all external forces. The isolated clement may be a whole structure or some part of it. </p><p>　　For example. Figure 4.1a shows an entire structure-a beamand-eolumn rigid bent-and the ext

15、ernal forces (represented by arrows). which include gravity. wind. and the reactive resistance of the supports (called the reactions). Note: Such a force system holds the structure in static equilibrium. </p><

16、p>　　Figure 4.lb is a free-body diagram of a single beam from the bent. Operating on the beam are two forces: its own weight and the interaction between the beam ends and the columns 10 which the beam is all ached. The

17、se interactions are not visible in the Ireebody diagram of the whole bent. so one purpose of the diagram for the beam is to illustrate these interactions. For example. note that the columns transmit to theendsofthe beam

18、s horizontal and vertical forces as well as rotational bending act</p><p>　　Figure 4.lc shows an isolated portion ofthe beam length. illustrating the beam's internal force actions. Operating on this fr

19、ee body arc its own weight and the actions of the beam segments on the opposite sides of the slicing planes. since it is these actions that hold the removed portion in place in the whole beam. </p><p>　　Figu

20、re 4.ld. a tiny segment. or particle. of the beam material is isolated, illustrating the interactions between this particle and those adjacent to it. This device helps designers visualize stress: in this case. due to its

21、 location in the beam. the particle is subjected to a combination of shear and linear compression stresses. </p><p>　　An exaggerated profile of a load-deformed structure helps establish the qualitative natur

22、e of the relationships between force actions and shape changes. Indeed. you can infer the form deformation from the type of force or stress. and vice versa. </p><p>　　FIGURE 4.1 Free-body diagrams.</p>

23、;<p>　　For example. Figure 4.la shows {he exaggerated deformation of the bent in Figure 4.1 under wind loading. Note how you can determine the nature of bending action in each member of the frame from this figure

24、. Figure 4.2b shows the nature of deformation of individual particles under various types of stress. </p><p>　　FIGURE 4.2 Structural deformation</p><p>　　The scaled plot is a graph of some mat

25、hematical relationship or real data. For example, the graph in Figure 4.3 represents the form of a damped ibration of an elastic spring. It consists of the plot of the displacements against elapsed time t. and represents

26、 the graph of the expression.</p><p>　　FIGURE 4.3 Graphical plot of a damped cyclic motion.</p><p>　　Although the equation is technically sufficient to describe the phenomenon, the graph illust

27、rates many aspects of the relationship. such as the rate of decay of the displacement. the interval of the vibration. the specific position at some specific elapsed time. and so on..</p><p>　　4.2 METHODS OF

28、 INVESTIGATION AND DESIGN </p><p>　　Traditional structural design centered on the working stress method. a method now referred to as stress design or allowable stress design (ASD). This method. which relies

29、on the classic theories of elastic behavior, measures a design's safety against two limits: an acceptable maximum stress (called allowable working stress) and a tolerable extent of deformation (deflection. stretch.

30、 erc.). These limits refer to a structure's response to service loads-that is. the loads caused by normal usage c</p><p>　　To convincingly establish stress. strain. and failure limits, tests were perform

31、ed extensively in the field (on real structures) and laboratories (on specimen prototypes. or models). Note: Real-world structural failures are studied both for research sake and to establish liability. </p><

32、p>　　In essence. the working stress method consists of designing a structure to work at some established percentage of its total capacity. The strength method consists of designing a structure tofail. but at a load co

33、ndition well beyond what it should experience. Clearly the stress and strength methods arc different. but the difference is mostly procedural.</p><p>　　The Stress Method (ASD) </p><p>　　The stre

34、ss method is as follows: </p><p>　　Visualize and quantify the service (working) load conditions as intelligently as possible. You can make adjustments by determining statistically likely load combinations (i

35、.e , dead load plus live load plus wind load). considering load duration. and so on. </p><p>　　Establish standard stress. stability, and deformation limits for the various structural responses-in tension. b

36、ending, shear, buckling. deflection, and so on. </p><p>　　Evaluate the structure's response. </p><p>　　An advantage of working with the stress method is that you focus on the usage condition

37、 (real or anticipated). The principal disadvantage comes from your forced detachment from real failure conditions-most structures develop much different forms of stress and strain as they approach their failure limits. &

38、lt;/p><p>　　The Strength Method (LRFD) </p><p>　　The strength method is as follows: </p><p>　　Quantify the service loads. Then multiply them by an adjustment factor'( essentially

39、a safety factor) to produce thejaclOred load. </p><p>　　Visualize the various structural responses and quantify the structure's ultimate (maximum, failure) resistance in appropriate terms (resistance to

40、 compression, buckling. bending. etc.). Sometimes this resistance is subject to an adjustment factor, called theresistancefacror. When you employ load and resistance factors. the strength method is now sometimes calle

41、d foad and resistancefaaor design (LRFD) (see Section 5.9). </p><p>　　Compare the usable resistance ofthe structu re to the u ltirnatc resistance required (an investigation procedure), or a structure with

42、an appropriate resistance is proposed (a design procedure). </p><p>　　A major reason designers favor the strength method is that structural failure is relatively easy to test. What is an appropriate working

43、condition is speculation. In any event, the strength method which was first developed for the design of reinforced concrete structures, is now largely preferred in all professional design work. </p><p>　　N

44、evertheless, the classic theories of clastic behavior still serve as a basis for visualizing how structures work. But ultimate responses usually vary from the classic responses, because of inelastic materials, secondary

45、effects, multi mode responses, and so on. In other words, the usual procedure is to first consider a classic, elastic response, and then to observe (or speculate about) what happens as failure limits are approached. <

46、/p><p><b>　　中文翻譯</b></p><p>　　4. 1結(jié)構(gòu)特性分析 </p><p>　　研究結(jié)構(gòu)的特性在結(jié)構(gòu)設(shè)計(jì)中是一個(gè)很重要的部分，它是保證設(shè)計(jì)安全性和適用性的 基礎(chǔ)。本節(jié)討論常用的結(jié)構(gòu)分析方法。正如貫穿本書所討論的一樣，本章集中講述與鋼結(jié) 構(gòu)設(shè)計(jì)相關(guān)的材料問題。</p><p><b>　　

47、1.分析的目的 </b></p><p>　　絕大數(shù)的結(jié)構(gòu)是因需而生的。因此，任何一個(gè)結(jié)構(gòu)的評(píng)價(jià)都是從分析結(jié)構(gòu)如何有效地滿足使用要求開始的。 </p><p>　　設(shè)計(jì)人員必須考慮以下三個(gè)因素：</p><p>　?。?）實(shí)用性指結(jié)構(gòu)的形式、構(gòu)造、耐久性、抗火性以及抗變形能力等的一般物理關(guān)系。</p><p>　　（2）可行性包括

48、造價(jià)、材料及產(chǎn)品的實(shí)用性和結(jié)構(gòu)的實(shí)用性。 </p><p>　　（3）安全性指抵抗設(shè)計(jì)荷載的能力。 </p><p><b>　　2.方法 </b></p><p>　　一個(gè)完整的結(jié)構(gòu)分析包括以下幾點(diǎn)：</p><p>　　（1）確定結(jié)構(gòu)的物理特性一一材料、形式、尺寸、方向、位置、支承條件以及內(nèi)部特征和構(gòu)造。</p

49、><p>　?。?）確定施加在結(jié)構(gòu)上的負(fù)荷.即荷載. </p><p>　　（3）確定結(jié)構(gòu)的變形極限。 </p><p>　　（4）確定結(jié)構(gòu)的荷載效應(yīng)，即荷載作用對(duì)結(jié)構(gòu)的內(nèi)力、應(yīng)力和主要變形的影響。 </p><p>　　（5）評(píng)定結(jié)構(gòu)是否能夠安全地承擔(dān)所需的結(jié)構(gòu)要求。 </p><p>　　結(jié)構(gòu)研究可以采用以下三種方法:

50、 </p><p>　?。?）圖解表示街載下結(jié)構(gòu)的變形。 </p><p>　?。?）使用數(shù)學(xué)模型。 </p><p>　?。?）對(duì)結(jié)構(gòu)或比例模型進(jìn)行試驗(yàn)，測量其在荷載下的效應(yīng). </p><p>　　當(dāng)需要精確的定量評(píng)定時(shí)，可以采用基于可靠度理論的數(shù)學(xué)模型或直接測量物理效 應(yīng)。-般地.建立數(shù)學(xué)模型先于實(shí)際結(jié)構(gòu).甚至是先于試驗(yàn)?zāi)Ｐ?。括?hào)直接測

51、定限制在試驗(yàn) 研究上或是限定在驗(yàn)證未被檢驗(yàn)過的理論上或是限定在設(shè)計(jì)方法土。 </p><p><b>　　3.直觀法 </b></p><p>　　本書強(qiáng)調(diào)圖解法，草圖是一種非常有價(jià)值的學(xué)習(xí)及解決問題的建助工具。最有用的三 種圖解法是:隔離體圖解法、荷載變形結(jié)構(gòu)放大示意圖和比例圖. </p><p>　　隔離體圖解法是用圖解的方法表示一個(gè)隔離單

52、元所受的所有外力.這個(gè)隔離單元可以 是整體結(jié)構(gòu)或是結(jié)構(gòu)的一部分。 </p><p>　　例如，圖4. 1（a）為一整體結(jié)構(gòu)——梁—柱剛性框架——和框架研受外力(由箭頭表示)。結(jié)構(gòu)所受的外力包括自重、風(fēng)荷載和支座反力(即反力)。注意：結(jié)構(gòu)所受的力系使結(jié)構(gòu)處于靜力平衡狀態(tài)。 </p><p>　　圖4. 1 （b）為從框架上隔離出來的單個(gè)梁的隔離體圖。該梁承受兩種力：自重以及梁端部和與梁相連碼

53、在之間的相互作用力。梁和柱之間的相互作用力在框架隔離體圖中是看不到的。因此梁的隔離體圖目的之一是闡明此相互作用力。注意：柱子傳遞給梁端的不僅有彎距，還有水平力和豎向力。 </p><p>　　圖4.1（c）為沿梁長度方向上部分梁的隔離體，給出了梁的內(nèi)力作用。在該隔離體上作用有自重和剖面相反一側(cè)對(duì)該梁段所施加的作用力，正是由于此內(nèi)力使得整個(gè)梁的剩余部分保持平衡。</p><p>　　圖4.1

54、（d）為梁截面隔離體中的一小段或一部分，該圖顯示了這部分與相鄰部分間的作用力。此圖有助于設(shè)計(jì)人員了解結(jié)構(gòu)所受的應(yīng)力。既然這樣，由于它是梁的一部分，因此受到剪應(yīng)力和線性壓應(yīng)力 的作用。</p><p>　　荷載—變形結(jié)構(gòu)放大示意圖有助于定性確定作用力和形狀改變之間的關(guān)系。實(shí)際上，可以從力或應(yīng)力的類型來推斷變形的形式，反之亦然。 </p><p>　　例如，圖4. 2（a）表示的是圖4. 1所

55、示框架在風(fēng)荷載作用下的變形放大示意圖。應(yīng)注意從圖中如何確定框架的每個(gè)構(gòu)件的彎曲作用特性。圖4.2 （b）給出了在不同類型應(yīng)力下，單個(gè)隔離體的變形特性。 </p><p>　　比例圖為一些數(shù)學(xué)關(guān)系或?qū)崪y數(shù)據(jù)的圖形。例如，圖4. 3代表一彈性彈簧阻尼振動(dòng)的形式。該圖是位移-時(shí)間（s-t）關(guān)系圖，其關(guān)系式如下: </p><p>　　雖然方程已經(jīng)足夠描述位移-時(shí)間的關(guān)系，但是圖示還可以表示位移-

56、時(shí)間關(guān)系的很多方面，比如位移衰減的比率，振動(dòng)周期以及在某一特定時(shí)間里振動(dòng)的具體位置等。 </p><p>　　4.2分析與設(shè)計(jì)方法 </p><p>　　傳統(tǒng)的結(jié)構(gòu)設(shè)計(jì)方法是圍繞著工作應(yīng)力法展開的，此方法現(xiàn)在稱為應(yīng)力設(shè)計(jì)或容許應(yīng)力設(shè)計(jì)（allowable stress design， ASD)。此方法依賴于經(jīng)典的彈性特性理論，用兩個(gè)極限值來衡量設(shè)計(jì)的安全性:可接受最大應(yīng)力(稱為容許工作應(yīng)力

57、)和容許的變形極限值(撓度、伸長等)。這兩個(gè)極限值是結(jié)構(gòu)在使用荷載下的效應(yīng)，即正常使用條件下的荷載效應(yīng)。 同時(shí)，承載力法是用來衡量設(shè)計(jì)是否足以抵抗其絕對(duì)荷載極限，即當(dāng)結(jié)構(gòu)必須破壞時(shí)，結(jié)構(gòu)抗力是否大于結(jié)構(gòu)效應(yīng)。 </p><p>　　為了得到令人信服的應(yīng)力極限值、應(yīng)變極限值以及破壞極限，大量進(jìn)行現(xiàn)場(在實(shí)際結(jié)構(gòu)上)和試驗(yàn)室(在結(jié)構(gòu)樣本原型或模型上)試驗(yàn)。 </p><p>　　提示 研究

58、實(shí)際結(jié)構(gòu)的破壞是為了研究和確定結(jié)構(gòu)的可靠性。 </p><p>　　實(shí)際上，工作應(yīng)力法是指設(shè)計(jì)一個(gè)結(jié)構(gòu)，使其在工作狀態(tài)下只發(fā)揮部分承載力。承載力法是設(shè)計(jì)一個(gè)結(jié)構(gòu)使其發(fā)生破壞，但是當(dāng)實(shí)際荷載沒有超過破壞荷載時(shí)，結(jié)構(gòu)不會(huì)發(fā)生破壞。顯而易見，應(yīng)力法和承載力法是不同的，但是這種不同主要是設(shè)計(jì)程序上的不同。</p><p>　　應(yīng)力法（ASD法） </p><p>　　應(yīng)力法

59、應(yīng)遵循以下規(guī)則： </p><p>　　（1） 盡可能合理地假設(shè)和確定使用（工作）荷載的狀況。可以通過確定可能的統(tǒng)計(jì)荷載組合（如恒載+活載+風(fēng)載）來調(diào)整荷載狀況，同時(shí)考慮荷載的持久性等。</p><p>　?。?） 確定不同結(jié)構(gòu)效應(yīng)下——受拉、受彎、受剪、屈曲及變形等的標(biāo)準(zhǔn)應(yīng)力、應(yīng)變和 變形極限值結(jié)構(gòu)效應(yīng)。 </p><p>　?。?） 評(píng)定結(jié)構(gòu)效應(yīng)。 </p

60、><p>　　使用應(yīng)力法的優(yōu)點(diǎn)是集中于結(jié)構(gòu)的使用狀態(tài)（真實(shí)的或期望的）。主要的不足之處在于人為的把破壞狀態(tài)分離出來——大多數(shù)結(jié)構(gòu)接近破壞極限時(shí)，應(yīng)力和應(yīng)變很不相同。 </p><p>　　承載力法（LRFD法） </p><p>　　承載力法應(yīng)遵循以下規(guī)則: </p><p>　?。?） 確定使用荷載值。然后乘以一修正系數(shù)（本質(zhì)上是一安全系數(shù)），

61、即得到設(shè)計(jì)荷載。 </p><p>　　（2） 假設(shè)結(jié)構(gòu)的各種效應(yīng)，并確定結(jié)構(gòu)在適當(dāng)效應(yīng)下的極限（最大或破壞）抗力（如受壓、屈曲及受彎等的抗力）。有時(shí)該抗力受到某一修正系數(shù)的影響，即抗力系數(shù)。在設(shè)計(jì)中使用了荷載和抗力系數(shù)，則承載力法有時(shí)又被稱為荷載抗力系數(shù)設(shè)計(jì)法(load and resistance factor design， LRFD) （見第4. 9節(jié)）。 </p><p>　?。?/p>

62、3） 對(duì)照結(jié)構(gòu)的使用抗力與極限設(shè)計(jì)抗力（分析過程），或建議采用適當(dāng)抗力的結(jié)構(gòu) （設(shè)計(jì)過程）。 </p><p>　　設(shè)計(jì)人員比較愿意使用承載力法的主要原因是結(jié)構(gòu)的破壞比較容易檢驗(yàn)。什么樣的工 作狀況才合適是一個(gè)值得思考的問題。無論如何，最初被用于設(shè)計(jì)鋼筋混凝土結(jié)構(gòu)的承載力法，現(xiàn)在己用于各專業(yè)設(shè)計(jì)。 </p><p>　　不過，經(jīng)典彈性理論作為基本方法仍然用于結(jié)構(gòu)工作狀況的假設(shè)上。但是，由于